1. Field of the Invention
The present invention relates to a swash-plate type variable-capacity type compressor for use in a vehicle air conditioner or the like.
2. Description of the Related Art
A compressor is incorporated in a refrigerating circuit, for a car air-conditioning system, for compressing coolant gas. A known swash plate type variable capacity type compressor comprises a housing having cylinder bores, a crank chamber, a suction chamber, and a discharge chamber formed therein, and pistons reciprocatingly arranged in the cylinder bores. A drive shaft is rotatably supported by the housing and driven by an external drive source, and a swash plate is supported by the drive shaft so that the swash plate is rotatable with the drive shaft and can incline with respect to the drive shaft, with shoes provided on the swash plate to convert the rotation of the drive shaft into the reciprocating motion of the pistons. In this compressor, a capacity control valve is provided for controlling the pressure in the crank chamber for changing a discharge capacity from the cylinder bores to the discharge chamber by the reciprocating motion of the pistons based on an inclination angle of the swash plate.
The conventional compressor is usually operatively coupled to a car engine as an external drive source via a belt and a magnetic clutch, so that the compressor is connected to the engine only when a refrigerating load occurs to effect a compressing operation.
However, if the magnetic clutch is provided in the compressor, problems arise in that the total weight increases, the production cost increases, and power is consumed for operating the magnetic clutch. To eliminate these drawbacks, there has recently been proposed a so-called clutchless swash plate type variable capacity type compressor which is directly coupled to an external drive source without a magnetic clutch interposed between the engine and the compressor, so that the compressor is normally driven while the external drive source is operating (for example, refer to Japanese Unexamined Patent Publication (Kokai) No. 10-205446). In the compressor disclosed in the above-described publication, a swash plate is arranged so that it can incline with respect to a drive shaft directly coupled to the external drive source, and a minimum inclination angle of the swash plate is maintained to provide a minimum discharge capacity. Therefore, in this compressor, it is possible to realize reduction of weight as well as to minimize power consumption of the external drive source, by directly coupling the compressor to the drive source without any magnetic clutch.
The problem of the conventional compressor is how to reduce power consumption of the external drive source. For example, power consumption reduction is required when the external drive source is being driven and the magnetic clutch is transferring the drive force of the external drive source, in the case where the magnetic clutch is provided and when the external drive source is being driven and the refrigerating function is stopped, for example, by turning off the operating switch of the car air conditioning device, in the case where the magnetic clutch is not provided.
That is, the control of the discharge capacity of the compressor is generally carried out by controlling the pressure (Pc) in the crank chamber using the capacity control valve. In particular, the inclination angle of the swash plate decreases and the discharge capacity decreases, when the pressure (Pc) in the crank chamber is raised by introducing the coolant gas from the discharge chamber having a high discharge pressure (Pd) into the crank chamber. On contrary, the inclination angle of the swash plate increases and the discharge capacity increases, when the pressure (Pc) in the crank chamber is lowered by introducing the coolant gas from the crank chamber into the suction chamber having the low suction pressure (Ps). In this constitution, it is necessary for the swash plate to be returned from the position of the minimum inclination angle to the position of the maximum inclination angle, when the pressure (Pc) in the crank chamber is lowered.
However, in the conventional compressor, if the minimum inclination angle is set to a value close to zero degrees, the compression action is not substantially carried out and the reaction force of the discharge pressure is not provided, so the swash plate is not assuredly returned to increase the inclination angle thereof. Therefore, it is not possible to set the minimum inclination angle to a value close to zero degrees in order to ensure the return of the swash plate to increase the inclination angle, and it is necessary to set the minimum inclination angle to a value in the range of 3 to 5 degrees, for example. In this way, it is necessary to maintain such a condition that the compression action of the compressor is slightly carried out even if the swash plate is at the minimum inclination angle, so that the reaction force of the discharge pressure contributes to return the swash plate to increase the inclination angle. By arranging the compressor in this way, the return of the swash plate to increase the inclination angle is ensured, in association with the decrease of the pressure (Pc) in the crank chamber.
In this case, when the swash plate is brought into the position of the minimum inclination angle, the swash plate continues to carry out the compressing action at the minimum inclination angle so that the reaction force of the discharge pressure normally acts on the swash plate, resulting in a problem that the power of the external drive source is consumed, even though it is small. It is therefore necessary to select the inclination angle of the swash plate during the minimum capacity operation to be as small as possible to provide the reaction force of the discharge pressure to reduce the power consumption of the air conditioning system while it is turned off, but it is not possible to return the swash plate from the minimum capacity operation (minimum inclination angle) if the reaction force of the discharge pressure is too small. In this manner, the reduction of the power consumption during the minimum capacity operation and securing returnability of the swash plate to increase the inclination angle are contradictory requirements, and it is necessary to control the minimum discharge capacity (minimum inclination angle) with high accuracy to meet these two requirements, so the production is difficult and the production costs increase.
In this connection, it is conceivable to arrange the compressor such that the minimum inclination angle is smaller than a limit angle at which the swash plate can be assuredly returned to increase the inclination angle by a reaction force of the discharge pressure, a return spring urging the swash plate so as to increase the inclination angle of the swash plate from the minimum inclination angle beyond the limit angle, and the urging force of the angle decreasing spring balancing with the urging force of the return spring at an angle greater than the limit angle. By this arrangement, it is possibly to satisfy two requirements, i.e., the reduction of the power consumption during the minimum capacity operation and securing returnability of the swash plate to increase the inclination angle, and it is not necessary to control the minimum discharge capacity (minimum inclination angle), and to realize the reduction of the production costs.
However, in experiments by the inventors, it was found that the above described advantageous effect is not satisfactory if the angle decreasing spring and the return spring are not appropriately selected. In particular, in the case where the discharge chamber is connected to the external refrigerating circuit via a check valve, it is important to allow the swash plate to increase the inclination angle, since the discharge pressure (Pd) is apt to be maintained constant and the discharge capacity can be more reliably and easily decreased.
In view of the above described prior art problems, an object of the present invention is to provide a swash plate type variable capacity type compressor by which the power consumption can be reduced, the swash plate can be assuredly returned to increase the inclination angle, and the production cost can be reduced.
According to one aspect of the present invention, there is provided a variable capacity type compressor comprising a housing having cylinder bores, a crank chamber, a suction chamber, and a discharge chamber formed therein. Pistons are reciprocatingly arranged in the cylinder bores, a drive shaft is rotatably supported by the housing and driven by an external drive source, and a swash plate is supported by the drive shaft so that the swash plate is rotatable with the drive shaft and can incline with respect to the drive shaft to convert the rotation of the drive shaft into the reciprocating motion of the pistons. A device such as a capacity control valve is arranged to control the pressure in the crank chamber for changing a discharge capacity, from the cylinder bores to the discharge chamber by the reciprocating motion of the pistons, based on an inclination angle of the swash plate. The swash plate is able to incline between a minimum inclination angle and a maximum inclination angle, the minimum inclination angle being smaller than a limit angle at which the swash plate can be assuredly returned in a direction to increase the inclination angle by a reaction force of the discharge pressure. An angle decreasing spring urges the swash plate so as to decrease the inclination angle of the swash plate from the maximum inclination angle toward the minimum inclination angle, and a return spring urges the swash plate so as to increase the inclination angle of the swash plate from the minimum inclination angle beyond the limit angle. The urging force of the angle decreasing spring balances the urging force of the return spring at an angle greater than the limit angle. A minimum spring load (F0) of the return spring applied to the swash plate at a minimum discharge capacity is greater than 20N.
In this compressor, the compressing action of the compressor becomes smaller or substantially zero while the swash plate is at the minimum inclination angle, so the power consumption of an external drive source is reduced. The swash plate can rotate at the inclination angle greater than the limit angle when the compressor is restarted since and the urging force of the angle decreasing spring balances with the urging force of the return spring, so that the swash plate can be reliably returned in the direction to increase the inclination angle.
In the inventor""s experiments, it has been found that an advantageous effect of the compressor can be ensured, as expected, if the minimum spring load (F0) of the return spring applied to the swash plate at a minimum discharge capacity is greater than 20N. The upper limit of the minimum spring load (F0) can be determined in accordance with the product of inertia of the swash plate and other members which rotate with the drive shaft, and the power consumption for driving the drive shaft becomes greater as far as a typical swash plate is used.
Also, according to another aspect of the present invention, there is provided a variable capacity type compressor comprising a fundamental arrangement similar to the above described compressor. The compressor in this embodiment includes the feature that a maximum spring load (F100) of the angle decreasing spring applied to the swash plate at a maximum discharge capacity is determined by the following relationship:
F100(N)=(180xc2x130)xe2x88x924xc3x97(VDxe2x88x92120)xe2x80x83xe2x80x83(1)
where VD is the displacement of the compressor.
In this compressor too, it has been found that an advantageous effect of the compressor can be ensured, as expected, if the maximum spring load (F100) is determined by the above described relationship. The upper limit of the maximum spring load (F100) is determined by the relationship, F100(N)=(180+30)xe2x88x924xc3x97(VDxe2x88x92120), and the lower limit of the maximum spring load (F100) is determined by the relationship, F100(N)=(180xe2x88x9230)xe2x88x924xc3x97(VDxe2x88x92120). The lower limit of the maximum spring load (F100) affects hunting of the swash plate.
Preferably, the angle decreasing spring is arranged around the drive shaft between a first fixed point and the swash plate, and the return spring urging the swash plate is arranged around the drive shaft between a second fixed point and the swash plate, the second fixed point being on the opposite side to the first fixed point with respect the swash plate.
Preferably, the compressor further comprises a lug plate fixed to the drive shaft in the crank chamber for rotation with the drive shaft, the swash plate being coupled to the lug plate so that the swash plate is rotatable with the lug plate and the swash plate is axially movable with respect to the lug plate, the lug plate providing the first fixed point.
Preferably, the compressor further comprises a circlip fixed to the drive shaft, the circlip providing the second fixed point.
Preferably, the discharge capacity when the urging force of the angle decreasing spring balances the urging force of the return spring is in the range from 3 to 10% of the maximum discharge capacity. In this constitution, the above described advantageous effect is further reliably ensured.
Preferably, the compressor is operatively coupled to an external drive source in a clutchless manner. In this case, the above described advantageous effect is further reliably ensured. In the clutchless compressor, the power is always transferred to the compressor as far as the external drive source is being driven, so the effect of reducing the power consumption is remarkable. Also, the weight of the compressor can be reduced.
Preferably, the compressor further comprises a check valve, the discharge chamber being connected to an external refrigerating circuit via the check valve. In this case, the effect of returning the swash plate is reliably ensured. In this compressor, it is possible to prevent the coolant gas from flowing in reverse, so it is possible to prevent the coolant liquid from staying in the compressor and to prevent an excessive rise in the pressure and the temperature in the compressor, to thereby improve durability of the compressor.
Preferably, the device controlling the pressure in the crank chamber comprises a first passage connecting the discharge chamber to the crank chamber, a second passage connecting the suction chamber to the crank chamber and a valve arranged in at least one of the first and second passages.